The invention discloses a UPS (Uninterrupted Power 
System), and the 
system comprises an air 
circuit breaker Q1, an air 
circuit breaker Q2, a maintenance bypass air switch Q3BP, a bypass static switch, a rectification module REC, an inversion module INV, an output 
isolation transformer TR2, a main circuit static switch, an air 
circuit breaker Q5, a contact-type normally-opened contact KM, and a storage battery. A main input circuit 
AC power supply is inputted from the air circuit breaker Q1, and the 
AC power supply is converted into a DC power supply through the rectification module REC, thereby completing the AC / DC conversion, so as to charge the storage battery in parallel connection with a main input circuit and to provide a reliable input 
direct current for the inversion module INV. The inversion module INV carries out the DC / AC conversion, and converts the DC power supply provided by the rectification module REC and the storage battery into the 
AC power supply. The AC power supply is outputted through the output 
isolation transformer TR2. A bypass input power supply is inputted from the air circuit breaker Q2, and is controlled by the bypass static switch and then is outputted. The UPS is stable in 
voltage, is quick and efficient, is simple in operation, and is convenient to maintain.